1. Field of the Invention
The present invention relates to an adhesive curing method, and more particularly, to an adhesive curing method suitable for curing an adhesive supplied between substrates of DVDs and other optical discs, and a curing apparatus.
2. Description of the Related Art
In general, DVDs and other optical discs employ a basic structure in which two transparent substrates are laminated with an adhesive. These substrates consist of those in which a recording layer that contains a reflective layer or semi-reflective layer is formed on one substrate only, or those in which a recording layer is formed on both substrates. In the case of those in which a recording layer is formed on one substrate only, there are those in which the thicknesses of both substrates are equal, and those in which the substrate on which the recording layer is not formed is in the form of a thin, transparent sheet. Moreover, there are also those that employ a structure in which four substrates are laminated by laminating two of the above laminated structures by means of an adhesive. In addition, examples of other structures include those in which a plurality of sheets transparent glass or lenses are laminated by means of an adhesive.
In such cases, in DVDs and other optical discs, after laminating two substrates by means of adhesive, the substrates are rotated at high speed to uniformly spread the adhesive between the substrates while also shaking off excess adhesive. Moreover, adhesive is typically cured in a short period of time by irradiating either one or both of the substrates with ultraviolet rays. Irradiation with ultraviolet rays is carried out by continuously irradiating with ultraviolet rays for a prescribed amount of time using a UV lamp, or irradiating with ultraviolet rays in pulses using a xenon lamp.
However, curing methods that use these lamps have the problems described below in all cases.    (1) In the case of using a UV lamp, since the emission efficiency is low and heat generation is extremely high, the substrates may be warped by the heat, or because an adequate heat dissipation mechanism is required, the apparatus becomes large and costs become high.    (2) Since UV lamps are expensive and have a short service life, in addition to resulting in high running costs, since they must be replaced every several tens of hours in the case of those having a particularly short service life, they also have a detrimental effect on productivity.    (3) In the case of irradiating with pulsed ultraviolet rays, although they are considerably advantageous in comparison with continuous irradiation in terms of heat, the impact during irradiation is large and due to vibrations at that time, glass or other adhered objects may be damaged or they may have a detrimental effect on the adhesion of the adhered object. In addition, there is also the possibility of the impact sound at that time resulting in noise that has a detrimental effect on the environment. Moreover, damping mechanisms and noise prevention mechanisms provided to solve these problems result in increased size of the apparatus and higher costs.    (4) In the case of using a xenon lamp, since the electrical power loss is extremely large, this is unsuitable both in terms of effects on the environment and costs.
In order to solve the above shortcomings of the prior art, the present invention is characterized by curing adhesive by irradiating with ultraviolet rays using a semiconductor element that emits ultraviolet rays, and more particularly, by using a light-emitting semiconductor element having a wavelength range in which the transmittance relative to the adhesive prior to curing is lower than the transmittance relative to the adhesive after curing.